The present invention relates to a judging method of loading condition of a vehicle with four wheels. Further, the present invention relates to a device for detecting whether the pressures of four wheels are simultaneously decreased or not in the vehicle with four wheels. More specifically, the present invention relates to a device for judging four-wheel diffusion by distinguishing a case of high loading on a vehicle.
There is a method of using the judging value of tire pressures based on the difference of the sums of rotational speeds of two pair of wheels which are located at the opposite corners of a vehicle, in order to detect that the tire pressures are decreased. However, the diffusion of one wheel or two wheels located at the opposite corners can be detected by the judging value of tire pressures, but it cannot be detected that the pressures of four wheels are simultaneously decreased.
The tire pressure is gradually lowered even if the tires are not damaged. Simultaneous decreased pressure occurs occasionally because air permeates the rubber of tires, in addition to simultaneous decreased pressure caused by the dimension growth of new tires. In such a case, the pressures of four wheels are often simultaneously decreased; therefore one happens to be not aware of the decreased pressure. When a vehicle runs while the air pressures of four tires are simultaneously decreased, there is danger of provoking the burst of tires at high speed running and gas mileage is also deteriorated; therefore there is also a concern over influence on the environment.
In order to alarm the four-wheel diffusion, there is a “load sensitivity method” which judges diffusion by utilizing rotational property (the difference of rolling=the difference of load fluctuation) at the decreased pressure of four wheels. The principle utilizes that the inclination of the acceleration to a lateral direction of a vehicle (hereinafter, referred to as Lateral G) to the judging value of tire pressures (hereinafter, referred to as DEL value) differs between at normal time and at the time of the four-wheel diffusion.
FIG. 1 is an example in which the Lateral G and DEL value are plotted in a case that tires are at normal air pressure and a case that the pressures of four wheels are decreased together by 40%. A regression straight line is calculated against a combination of the Lateral G and DEL value and its primary coefficient (inclination) is referred to as the load sensitivity. As shown in FIG. 1, the load sensitivity (the inclination of Lateral G to DEL value) differs between a case of normal air pressure and a case that the pressures of four wheels are decreased. Accordingly, when the load sensitivity is changed at a fixed value or more in comparison with the inclination of the normal air pressure, it can be detected that the pressures of four wheels are decreased.
However, the load sensitivity method is sensitive for a load as shown by its name, and the procedure shown in the fore-description is limited to a case that a load is nearly constant.
Further, there is a method of detecting four-wheel diffusion by measuring the load through providing a load sensor and correcting the load sensitivity in accordance with the load (Japanese Unexamined Patent Publication No. 145654/1996).